Projection unit for a level sensor, method of monitoring height of a substrate, and lithographic system comprising the projection unit
A projection unit for a level sensor, the projection unit including: a first light pipe having a first inlet configured to receive radiation from a source and a first outlet; and a second light pipe having a second inlet configured to receive the radiation from the first light pipe and a second outlet. The unit may include a lens device configured to receive radiation from the second outlet and to output radiation having a predetermined distribution of intensity and irradiance.
1 . A projection unit for a level sensor, the projection unit comprising:
a first light pipe having a first inlet configured to receive radiation from a source and a first outlet;
a second light pipe having a second inlet configured to receive the radiation from the first light pipe and a second outlet;
a lens system configured to receive radiation from the second outlet and to output radiation having a predetermined distribution of intensity and irradiance;
a grating arranged to be illuminated by the radiation exiting the lens system, the grating comprising an array of grating units, each grating unit comprising a number of slits having a predetermined size to filter the radiation; and
an image multiplier device arranged to receive radiation exiting the grating, the radiation exiting the grating having an aspect ratio, and the image multiplier device configured to increase the aspect ratio.
2 . The projection unit of claim 1 , wherein the lens system has a focal point on one side located at the second outlet.
3 . The projection unit of claim 1 , wherein the first light pipe has tapering walls, and wherein a width and height of the first inlet exceeds a width and height of the first outlet.
4 . The projection unit of claim 1 , wherein the first light pipe is symmetrical along its longitudinal axis.
5 . The projection unit of claim 1 , wherein the second light pipe has tapering walls, and wherein a width and height of the second outlet exceeds a width and height of the second inlet.
6 . The projection unit of claim 1 , wherein the grating units are rectangular, and the slits are arranged obliquely with respect to sides of the respective grating unit.
7 . The projection unit of claim 1 , wherein the radiation exiting the projection grating has an aspect ratio of width to height of at least 1:1.5, and the image multiplier device is configured to increase the aspect ratio to at least 1:2.
8 . The projection unit of claim 1 , further comprising:
a light module comprising a light source to produce the radiation; and
a light guide configured to receive the radiation from the light module and transfer the radiation to the first light pipe.
9 . The projection unit of claim 8 , wherein the light guide is a single multimode fiber.
10 . A lithographic system comprising a level sensor for measuring height of a substrate, the level sensor comprising the projection unit according to claim 1 .
11 . A method of monitoring height of a substrate, the method comprising:
receiving radiation from a radiation source into a first light pipe of a projection unit of a level sensor, wherein at least some of the radiation reflects off an interior of the first light pipe;
receiving radiation exiting the first light pipe into a second light pipe of the projection unit of the level sensor, wherein at least some of the radiation reflects off an interior of the second light pipe; and
providing the radiation from the second light pipe toward the substrate for monitoring of the height of the substrate.
12 . The method of claim 11 , further comprising using a lens system to receive radiation exiting the second light pipe, the lens system configured to output radiation having a predetermined distribution of intensity and irradiance.
13 . The method of claim 12 , wherein the lens system has a focal point on one side located at an outlet of the second light pipe.
14 . The method of claim 11 , further comprising illuminating a grating by the radiation exiting the lens system, the grating comprising an array of grating units, each grating unit comprising a number of slits having a predetermined size to filter the radiation.
15 . The method of claim 14 , wherein the radiation exiting the grating has an aspect ratio and further comprising increasing the aspect ratio using an image multiplier device arranged to receive radiation exiting the grating.
16 . The method of claim 15 , wherein the radiation exiting the projection grating has an aspect ratio of width to height of at least 1:1.5, and comprising increasing the aspect ratio to at least 1:2 using the image multiplier device.
17 . The method of claim 14 , wherein the grating units are rectangular, and the slits are arranged obliquely with respect to sides of the respective grating unit.
18 . The method of claim 11 , wherein the first light pipe has tapering walls, and wherein a width and height of an inlet of the first light pipe exceeds a width and height of an outlet of the first light pipe.
19 . The method of claim 11 , wherein the second light pipe has tapering walls, and wherein a width and height of the second outlet exceeds a width and height of the second inlet.
20 . A projection unit for a level sensor, the projection unit comprising:
a first light pipe having a first inlet configured to receive radiation from a source and a first outlet;
a second light pipe having a second inlet configured to receive the radiation from the first light pipe and a second outlet;
a lens system configured to receive radiation from the second outlet and to output radiation having a predetermined distribution of intensity and irradiance;
a grating arranged to be illuminated by the radiation exiting the lens system and configured to provide the radiation toward a substrate for measurement by the level sensor.